The effect of solvent and proton donor type on the conductivity and physico-chemical properties of poly(vinylidene fluoride)-based proton-conducting gel electrolytes

In the present work proton-conducting gels based on commercially available poly(vinylidene fluoride) (PVdF) system are studied. The polymer, H3PO4 and phosphoric acid organic esters (used as proton donors) are dissolved in dimethylformamide (DMF) or dimethyl acetate (DMA) at ambient temperatures and than cast on the flat glass substrate. Highly conducting (∼10−3 S cm−1 at 20°C) colorless polymeric membranes are obtained in a relatively narrow PVdF and proton donor concentration ranges. The highest conductivities have been obtained when phosphoric acid esters are used as proton donors. Conductivities measured for systems containing DMF are slightly higher than for DMA-based derivatives. The gel electrolytes studied are thermally stable up 100°C as shown by the DSC experiments. The interactions between H3PO4 and solvents used are studied by means of FT-IR spectroscopy which shows the possibility of the protonation of solvent molecules by H3PO4. Therefore, the possibility of proton transportation via the Grotthus-type mechanism cannot be excluded.